1. Technical Field of the Invention
The present invention relates to RF strip transmission lines, and more particularly, to a flexible RF strip transmission line constructed of flexible dielectric and ground plane materials to form a stripline structure.
2. Description of Related Art
The continued downsizing of mobile telephone hardware and the development of such features as the "flip" phone wherein a mobile telephone has a portion which folds over another portion of the phone in order to conserve space have generated a variety of problems. The decreased amount of space within a mobile telephone has required the need for the various transmission lines running through the mobile telephone to be folded prior to fixed installation in order to conserve space. Also within the "flip" type mobile telephones, transmission lines running from the main portion of the mobile telephone to the "flip" portion must have the ability to be repeatedly flexed between open and closed positions without destroying the integrity of the transmission lines passing between the two sections.
Current practice involves the use of either coaxial cable or planar stripline structures having a ground plane formed with copper foil or relatively rigid metalization systems. Both of these practices suffer from various shortcomings. Coaxial cables require the use of a separate cable for each signal being transmitted. This requires the installation and routing of each cable and takes a great deal of time. Furthermore, each cable must be individually connected to the mobile telephone circuitry. The use of coaxial cables and connectors requires a great deal of space which is at a premium within smaller mobile telephone models.
Traditional planar stripline systems may not be folded or used within a "flip" portion of a mobile telephone since the metalization employed in forming the upper and lower ground plane is too rigid to enable continuous flexing of the ground planes between the open and closed positions of the "flip" portion. Currently available planar stripline structures can employ patterned openings within the ground plane metalization to enable a degree of flexibility, but this solution limits the effectiveness of the shielding.
Thus, each of the previously used fabrication methods includes significant shortcomings in RF performance, space limitations and manufacturing costs. Ideally, the shielding effectiveness for a transmission line in a mobile telephone should be as close as possible to the shielding of a coaxial cable and be implemented with the fewest elements possible.